Method for producing slit separator and method for producing separator roll

ABSTRACT

A good-quality slit separator having a small amount of fuzziness at a slit part thereof is to be obtained. The present invention includes: a step (S 101 ) of conveying an original sheet (S); and a step (S 102 ) of slitting the original sheet (S) by causing a plurality of slitting blades ( 72 ) to cut into the original sheet (S) such that tangent plane angles (θ 3 ) in a tangent plane, on which a slitting position is in contact with the original sheet (S), are substantially identical with each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a section 371 of International Application No.PCT/JP2015/085842, filed Dec. 22, 2015, which was published in theJapanese language on Jun. 30, 3016, under International Publication No.WO2016/104507A1, and the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention, relates to (i) a method for producing a porousslit separator to be used for a battery such as a lithium-ion secondarybattery, (ii) a method for producing a separator roll, which methodemploys the method for producing the porous slit separator, (iii) amethod for slitting a separator, and (iv) a separator slittingapparatus.

BACKGROUND ART

A battery separator needs to be produced so as to have a width(hereinafter, referred to as “product width”) that is suitable for abattery to be produced with the use of the separator. However, it is notefficient to produce a separator having such a product width at the timeof production. Therefore, it is general practice to prepare a separatororiginal sheet having a wide width, and then to simultaneously produce,by slitting the separator original sheet, a plurality of separators eachhaving the product width.

Patent Literature 1 discloses a spot-type carbon dioxide laser cuttingdevice as a device to slit a separator. Patent Literature 1 teachesusing (i) a carbon dioxide laser oscillation unit and (ii) a mirror(s)for bending a laser beam (see paragraph [0050]).

Patent Literature 2 discloses a method for slitting a separator, whichmethod employs a configuration in which a prescribed relationship ismade between an angle between a razor blade and the separator and (ii) athickness of the separator. Patent Literature 1 teaches that theconfiguration of Patent Literature 2 makes it unlikely that theseparator would have pores and tears (see paragraph [0030]).

Note that a separator before being slit is referred to as “originalsheet”. Note also that a separator(s) after being slit is referred to as“slit separator”.

CITATION LIST Patent Literature

[Patent Literature 1]

Japanese Patent Application Publication Tokukai No. 2013-119094(Publication date: Jun. 17, 2013)

[Patent Literature 2]

Japanese Patent Application Publication Tokukai No. 2002-273684(Publication date: Sep. 25, 2002)

SUMMARY OF INVENTION Technical Problem

However, the device disclosed in Patent Literature 1 requires including(i) the carbon dioxide laser oscillation unit and (ii) a mirror(s) forbending a laser beam. This causes the device to be large in size. Themirror, in particular, is required to be provided at each position atwhich the original sheet is slit. This makes it more difficult to usethe device with a larger number of slit separators into which theoriginal sheet is to be slit.

It can be said that the method disclosed in Patent Literature 2 can beused relatively easily even in a case where there is an increase in thenumber of slit separators into which the original sheet is slit.However, quality of a slit separator is not radically affected by (i)the angle between the razor blade and the separator or (ii) thethickness of the separator. Therefore, a good-quality slit separator isnot necessarily obtained by use of the method of Patent Literature 2.

The original sheet is slit, by a plurality of slitting blades aligned ina width direction of the original sheet. However, Patent Literatures 1and 2 do not teach a configuration for obtaining a good-quality slitseparator with vise of a plurality of slitting blades.

The present invention has been made in view of the problem, and it is anobject of the present invention to provide (i) a method for producing aslit separator, and (ii) a method for producing a separator roll, eachof which method allows a good-quality slit separator and a good-qualityseparator roll to be obtained.

Solution to Problem

In order to attain the object, a slit separator production method inaccordance with Aspect 1 of the present invention includes: a conveyingstep of conveying a battery separator original sheet which is porous;and a first slitting step of slitting the battery separator originalsheet by causing a plurality of slitting blades to cut into the batteryseparator original sheet such that a plurality of slitting blade edgeangles in a tangent plane, on which a slitting position is in contactwith the battery separator original sheet, are substantially identicalwith each other.

A separator roll production method in accordance with Aspect 2 of thepresent invention includes: each of the steps recited in the slitseparator production method; and a winding step of winding, around acore, a separator obtained by slitting the battery separator originalsheet.

Advantageous Effects of Invention

Each of the aspects of the present invention brings about such an effectthat it is possible to obtain, all at once, (i) a plurality ofgood-quality slit separators having a small amount of fullness at a slitpart thereof and (ii) a good-quality separator roll having a side endsurface on which there is a small amount of fuzziness.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating a cross sectional configurationof a lithium-ion secondary battery.

FIG. 2 is a schematic view illustrating details of the configuration ofthe lithium-ion secondary battery illustrated in FIG. 1.

FIG. 3 is a schematic view illustrating another configuration of thelithium-ion secondary battery illustrated in FIG. 1.

FIG. 4 is a schematic view illustrating a configuration of a slittingapparatus for slitting the separator.

FIG. 5 is a combination of a side view and a front view illustrating aconfiguration of a cutting device of the slitting apparatus illustratedin FIG. 4.

FIG. 6 is a schematic view illustrating a separator slitting method inaccordance with Embodiment 1.

FIG. 7 is a combination of a front view and a cross-sectional viewillustrating a configuration of each of slitting blades for use in theseparator slitting method illustrated in FIG. 6.

FIG. 8 is a combination of a front view and cross-sectional viewsillustrating details of the configuration of the slitting bladeillustrated in FIG. 7.

FIG. 9 is a set of schematic views illustrating a relationship between(i) a cross-sectional angle and a mounting angle of the slitting bladeillustrated in FIG. 8 and (ii) a tangent-plane blade edge angle.

FIG. 10 is a front view illustrating a configuration of a slitting bladefor use in a separator slitting method in accordance with Embodiment 2.

FIG. 11 is a set of cross-sectional views illustrating a configurationof a slitting blade which is different from the slitting bladeillustrated in FIG. 10.

FIG. 12 is a front view illustrating a separator slitting method whichis different from the separator slitting method in which the slittingblade illustrated in FIG. 10 is used.

FIG. 13 is a front view illustrating another separator slitting methodwhich is different from the separator slitting method in which theslitting blade illustrated in FIG. 10 is used.

FIG. 14 is a set of cross-sectional views illustrating a configuration,when viewed from a side, of the slitting blades which are lower bladesof pairs of slitting blades for use in the separator slitting methodillustrated in FIG. 13.

FIG. 15 is a set of views for describing how fuzziness occurs on aseparator and a separator roll.

FIG. 16 is a set of schematic views each illustrating a configurationfor maintaining consistent tangent-plane blade edge angles among aplurality of slitting blades in Embodiment 4.

FIG. 17 is a schematic view describing a configuration for makingtangent-plane blade edge angles of slitting blades substantiallyidentical with each other.

DESCRIPTION OF EMBODIMENTS

[Common Configuration]

The following discusses in order a lithium-ion secondary battery, aseparator, a heat resistant separator, a method for producing the heatresistant separator, a slitting apparatus, and a cutting device whichare common to Embodiments discussed late.

(Lithium-Ion Secondary Battery)

A nonaqueous electrolyte secondary battery, typically, a lithium-ionsecondary battery has a high energy density, and therefore, currentlywidely used not only as batteries for use in devices such as personalcomputers, mobile phones, and mobile information terminals, and for usein moving bodies such as automobiles and airplanes, but also asstationary batteries contributing to stable power supply.

FIG. 1 is a schematic view illustrating a cross sectional configurationof a lithium-ion secondary battery 1.

As illustrated in FIG. 1, the lithium-ion secondary battery 1 includes acathode 11, a separator 12, and an anode 13. Between the cathode 11 andthe anode 13, an external device 2 is connected outside the lithium-ionsecondary battery 1. Then, while the lithium-ion secondary battery 1 isbeing charged, electrons move in a direction A. On the other hand, whilethe lithium-ion secondary battery 1 is being discharged, electrons movein a direction B.

(Separator)

The separator 12 is provided so as to be sandwiched between the cathode11 which is a positive electrode of the lithium-ion secondary battery 1and the anode 13 which is a negative electrode of the lithium-ionsecondary battery 1. The separator 12 is a porous film that separatesthe cathode 11 and the anode 13, allowing lithium ions to move betweenthe cathode 11 and the anode 13. The separator 12 contains, for example,polyolefin such as polyethylene or polypropylene as a material.

FIG. 2 is a schematic view illustrating details of the configuration ofthe lithium-ion secondary battery 1 illustrated in FIG. 1. (a) of FIG. 2illustrates a normal configuration. (b) of FIG. 2 illustrates a state inwhich a temperature of the lithium-ion secondary battery 1 has risen,(c) of FIG. 2 illustrates a state in which a temperature of thelithium-ion secondary battery 1 has sharply risen.

As illustrated in (a) of FIG. 2, the separator 12 is provided, with manypores P. Normally, lithium ions 3 in the lithium-ion secondary battery 1can move back and forth through the pores P.

However, there are, for example, cases in which the temperature of thelithium-ion secondary battery 1 rises due to excessive charging of thelithium-ion secondary battery 1, a high current caused byshort-circuiting of the external device, or the like. In such cases, theseparator 12 melts or softens and the pores P are blocked as illustratedin (b) of FIG. 2. As a result, the separator 12 shrinks. This stops theabove movement of the lithium ions 3, and consequently stops the abovetemperature rise.

However, in a case where a temperature of the lithium-ion secondarybattery 1 sharply rises, the separator 12 suddenly shrinks. In thiscase, as illustrated in (c) of FIG. 2, the separator 12 may bedestroyed. Then, the lithium ions 3 leak out from the separator 12 whichhas been destroyed. As a result, the lithium ions 3 do not stop moving.Consequently, the temperature continues rising.

(Heat Resistant Separator)

FIG. 3 is a schematic view illustrating another configuration of thelithium-ion secondary battery 1 illustrated in FIG. 1. (a) of FIG. 3illustrates a normal configuration, and (b) of FIG. 3 illustrates astate in which a temperature of the lithium-ion secondary battery 1 hassharply risen.

As illustrated in (a) of FIG. 3, the separator 12 can be a heatresistant separator that includes a porous film 3 and a heat resistantlayer 4. The heat resistant layer 4 is laminated on a surface of theporous film 5 which surface is on a cathode 11 side. Note that the heatresistant layer 4 can alternatively be laminated on a surface of theporous film 5 which surface is on an anode 13 side, or both surfaces ofthe porous film 5. Further, the heat resistant layer 4 is provided withpores which are similar to the pores P. Normally, the lithium ions 3move back and forth through the pores P and the pores of the heatresistant layer 4. The heat resistant layer 4 contains, for example,wholly aromatic polyamide (aramid resin) as a material.

As illustrated in (b) of FIG. 3, even in a case where the temperature ofthe lithium-ion secondary battery 1 sharply rises and as a result, theporous film 5 melts or softens, the shape of the porous film 5 ismaintained because the heat resistant layer 4 supports the porous film5. Therefore, such a sharp temperature rise results in only melting orsoftening of the porous film 5 and consequent blocking of the pores P.This stops movement of the lithium ions 3 and consequently stops theabove-described excessive discharging or excessive charging. In thisway, the porous film 5 can be prevented from being destroyed.

(Production Steps of the Heat Resistant Separator)

How to produce the heat resistant separator of the lithium-ion secondarybattery 1 is not specifically limited. The heat resistant separator 12can be produced by a well-known method. The following discussion assumesa case where the porous film 5 contains polyethylene as a main material.However, even in a case where the porous film 5 contains anothermaterial, the similar steps can still be applied to production of theseparator 12.

For example, it is possible to employ a method including the steps offirst forming a film by adding a plasticizer to a thermoplastic resin,and then removing the plasticizer with an appropriate solvent. Forexample, in a case where the porous film 5 is made of a polyethyleneresin containing ultrahigh molecular weight polyethylene, it is possibleto produce the porous film 5 by the following method.

This method includes (1) a kneading step of obtaining a polyethyleneresin composition by kneading a ultrahigh molecular weight polyethyleneand an inorganic filler such as calcium carbonate, (2) a rolling step offorming a film with the polyethylene resin composition, (3) a removalstep of removing the inorganic filler from the film obtained in the step(2), and (4) a stretching step of obtaining the porous film 5 bystretching the film obtained in the step (3).

In the removal step, many fine pores are provided in the film. The finepores of the film stretched in the stretching step become theabove-described pores P. The porous film 5 formed as a result is apolyethylene microporous film having a prescribed thickness and aprescribed air permeability.

Note that in the kneading step, 100 parts by weight of the ultrahighmolecular weight polyethylene, 5 parts by weight to 200 parts by weightof a low-molecular weight polyolefin having a weight-average molecularweight of 10000 or less, and 100 parts by weight to 400 parts by weightof the inorganic filler can be kneaded.

Thereafter, in a coating step, the heat resistant layer 4 is formed on asurface of the porous film 5. For example, on the porous film 5, anaramid/NMP (N-methylpyrrolidone) solution (coating solution) is applied,and thereby, the heat resistant layer 4 that is an aramid heat resistantlayer is formed. The heat resistant layer 4 can be provided on only onesurface or both surfaces of the porous film 5. Alternatively, forcoating, the heat resistant layer 4 can he formed by using a mixedsolution containing a filler such as alumina/carboxymethyl cellulose.

A method for coating the porous film 5 with a coating solution is notspecifically limited as long as uniform wet coating can be performed bythe method. The method can be a conventionally well-known method such asa capillary coating method, a spin coating method, a slit die coatingmethod, a spray coating method, a dip coating method, a roll coatingmethod, a screen printing method, a flexo printing method, a bar coatermethod, a gravure coater method, or a die coater method. The heatresistant layer 4 has a thickness which can be controlled by (i) athickness of a coating wet film and (ii) a solid-content concentrationin the coating solution.

It is possible to use a resin film, a belt, a metal drum or the like asa support with which the porous film 5 is fixed or transferred incoating.

As described above, it is possible to produce the separator 12 (heatresistant separator) in which the heat resistant layer 4 is laminated onthe porous film 5. Thus produced separator is wound on a cylindricalcore. Note that a subject to be produced by the above production methodis not limited to the heat resistant separator. The above productionmethod does not necessarily include the coating step. In a case wherethe method includes no coating step, the subject to be produced is aseparator including no heat resistant layer.

(Slitting Apparatus)

The heat resistant, separator or the separator including no heatresistant layer (hereinafter, referred to as “separator”) preferably hasa width (hereinafter, referred to as “product width”) suitable forapplication products such as the lithium-ion secondary battery 1.However, for improving productivity, the separator is produced so as tohave a width that is equal to or larger than a product width. Then,after having been once produced so as to have a width equal to or largerthan the product width, the separator is slit into a separator(s) havingthe product width.

Note that the “separator width” means a dimension of the separator in adirection perpendicular to a lengthwise direction and a thicknesswisedirection of the separator. In the description below, a wide separatorhaving not yet been slit is referred to as an “original sheet” whileparticularly a separator having been slit is referred to as a “slitseparator”. Note also that slitting means to slit the separator in thelengthwise direction (flow direction of the film during production; MD:Machine direction), and that cutting means to slit the separator in atransverse direction (TD). The transverse direction (TD) means adirection which is substantially perpendicular to the lengthwisedirection (MD) and the thicknesswise direction of the separator.

FIG. 4 is a schematic view illustrating a configuration of a slittingapparatus 6 for slitting the separator. (a) of FIG. 4 illustrates anentire configuration, and (b) of FIG. 4 illustrates an arrangementbefore and after slitting the original sheet.

As illustrated in (a) of FIG. 4, the slitting apparatus 6 includes arotatably-supported cylindrical wind-off roller 61, rollers 62 to 69,and take-up rollers 70U and 70L. The slitting apparatus 6 is furtherprovided with cutting devices 7 described later.

(Before Slitting)

In the slitting apparatus 6, a cylindrical core c on which the originalsheet is wrapped is fit on the wind-off roller 61. As illustrated in (b)of FIG. 4, the original sheet is wound off from the core c to a route Uor L. Thus unwound original sheet is conveyed to the roller 68 via therollers 63 to 67. In the step of conveying the unwound original sheet,the original sheet is slit into slit separators. Note that the roller 67does not need to be provided. In such a case, the original sheet isconveyed from the roller 64 to the roller 68.

(After Slitting)

As illustrated in (b) of FIG. 4, some of the slit separators are woundon cylindrical cores u (bobbins) fit on take-up rollers 70U,respectively. Meanwhile, the others of the slit separators are wound oncylindrical cores 1 (bobbins) fit on take-up rollers 70L, respectively.Note that each of combinations of the slit separators each wound into aroll form and the corresponding cores u and 1 is referred to as a“roll”.

(Cutting Device)

FIG. 5 is a view illustrating a configuration of each of the cuttingdevices 7 of the slitting apparatus 6 as illustrated in (a) of FIG. 4.(a) of FIG. 5 is a side view of the cutting device 7, and (b) of FIG. 5is a front view of the cutting device 7.

As illustrated in (a) and (b) of FIG. 5, each of the cutting devices 7includes a holder 71 and a slitting blade 72. The holder 71 is fixed toa housing or the like provided in the slitting apparatus 6. The holder71 holds the slitting blade 72 in a manner such that the slitting blade72 and the original sheet of the separator being conveyed have a fixedpositional relation. The slitting blade 72 (i) has a finely sharpenededge and (ii) slits the original sheet of the separator by using theedge.

[Embodiment 1]

The following discusses an embodiment of the present invention withreference to FIGS. 6 to 9.

<Separator Slitting Method>

(Cutting of Original Sheet by Slitting Blade)

FIG. 6 is a schematic view illustrating a separator slitting method inaccordance with Embodiment 1. (a) of FIG. 6 is a front view. (b) of FIG.6 is a top view.

As illustrated in (a) of FIG. 6, an original sheet S is conveyed along aset conveyance route up to the blade edges of the slitting blades 72.The slitting blades 72 slit the original sheet S into slit separators suand slit separators s1. The slit separators su and the slit separatorss1 are conveyed in respective directions.

As illustrated in (b) of FIG. 6, the original sheet S is conveyed in asingle direction D. The slitting blades 72 cut in the original sheet S(i) parallel to the direction D and (ii) perpendicularly to the originalsheet S.

The original sheet S is a separator immediately before being slit by theslitting blades 72.

(Cross-Sectional Angle of Slitting Blade)

FIG. 7 is a view illustrating a configuration of each of the slittingblades 72 for use in the separator slitting method illustrated in (a)and (b) of FIG. 6. (a) of FIG. 7 is a front view. (b) of FIG. 7 is across-sectional view taken along the line A-A. illustrated in (a) ofFIG. 7.

As illustrated in (a) of FIG. 7, the slitting blade 72 includes theLinear blade edge E. As illustrated in (b) of FIG. 7, the shape of theslitting blade 72 is plane-symmetrical with respect to a plane a whichis perpendicular to the original sheet S and to the cross section takenalong the line A-A (hereinafter, referred to as “A-A cross section”).Then, in the A-A cross section, the slitting blade 72 expands from theblade edge E as a tip so as to have a prescribed angle. Across-sectional angle θ₁ of the cross section perpendicular to the bladeedge E is, for example, 25°.

(Mounting Angle of Slitting Blade)

FIG. 8 is a set of views illustrating details of the configuration ofthe slitting blade 72 illustrated in (a) and (b) of FIG. 7. (a) of FIG.8 is a front view. (b) of FIG. 8 is a cross-sectional view taken alongthe line B-B in (a) of FIG. 8. (c) of FIG. 8 is a cross-sectional viewtaken along the line A-A in a case where the slitting blade 72 is atwo-stage edge. (d) of FIG. 8 is a flow chart, illustrating theseparator slitting method in which the slitting blade 72 is used.

As illustrated in (a) of FIG. 8, the slitting blade 72 is mounted at aprescribed angle with respect to the original sheet S. A mounting angleθ₂ is, for example, 12.8°.

A cross section taken along the line B-B (hereinafter, referred to as“B-B cross section”) is a tangent plane on which a slitting position ofthe slitting blade 72 in contact with the original sheet S.

(Tangent-Plane Blade Edge Angle of Slitting Blade)

As illustrated in (b) of FIG. 8, in the cross section T (tangent plane)which is the B-B cross section, the slitting blade 72 expands from theblade edge E as a tip so as to have a prescribed angle. The angle is across-sectional angle on a plane including the original sheet S withwhich the blade edge E is in contact (the angle is hereinafter referredto as “tangent-plane blade edge angle”). The inventors found that thetangent-plane blade edge angle largely affects quality of a slitseparator. In a case where the tangent-plane blade edge angle θ₃ is in arange of not less than 3° to not more than 35° (hereinafter, referred toas “range α”), it is possible to obtain a good-quality slit separatorhaving a small amount of fuzziness at a slit part thereof.

(Two-Stage Edge)

As illustrated in (c) of FIG. 8, the slitting blades 72 can each be atwo-stage edge. The blade edge E of the two-stage edge expands at across-sectional angle θ₁ (first stage), and then expands at across.-sectional angle θ₄ which is narrower than the cross-sectionalangle θ₁ (second stage). Even in a case of the two-stage edge, thetangent-plane blade edge angle θ₃ can be calculated as described abovein a small area indicated by an area F.

(Flow of Separator Slitting Method)

As illustrated in (d) of FIG. 8, the separator slitting method inaccordance with Embodiment 1 includes (i) a step S101 of conveying theoriginal sheet S and (ii) a step S102 of slitting the original sheet S.In so doing, the tangent-plane blade edge angle θ₃ falls within therange α.

(Relationship Between (i) Cross-Sectional Angle and Mounting Angle and(ii) Tangent-Plane Blade Edge Angle)

(a) through (d) of FIG. 9 are a set of schematic views illustrating arelationship between (i) the cross-sectional angle θ₁ and the mountingangle θ₂ of the slitting blade 72 illustrated in (a) and (b) of FIG. 8and (ii) the tangent-plane blade edge angle θ₃ of the slitting blade 72illustrated in (a) and (b) of FIG. 8. Points e to i shown in (a) through(d) of FIG. 9 respectively correspond to points e to i shown in (a)through (d) of FIG. 8.

As illustrated in (a) of FIG. 9, the blade edge E can be regarded as atriangular prism within a small area (e.g. the area F described above).Hereinafter, the blade edge E will be referred to as “triangular prism”.

(Cross-Sectional Angle and Mounting Angle)

As illustrated in (b) of FIG. 9, the above-described cross-sectionalangle θ₁ corresponds to an angle at the point g of a triangle having thepoints f, g and h which are vertices of the triangular prism. Thefollowing Formula (1) concerning the cross-sectional angle θ₁ can beobtained:z/2=m·tan(θ₁/2)  Formula (1)where (i) the point i is a middle point between the points f and h, (ii)a length of a side between the points f and h is z, and (iii) a lengthof a line segment between the points g and i is m.

As illustrated in (c) of FIG. 9, the above-described mounting angle θ₂corresponds to an angle at the point e of a triangle having (i) thepoints e and g which are vertices of the triangular prism and (ii) thepoint i. The following Formula (2) concerning the mounting angle θ₂ canbe obtained:m/n=sin(θ₂)  Formula (2)where a length of a side between the points e and i is n.(Tangent-Plane Blade Edge Angle)

(d) of FIG. 9 illustrates the cross section T illustrated in (b) of FIG.8. Then, the following Formula (3) concerning the tangent-plane bladeedge angle θ₃ can be obtained:tan(θ₃/2)=(z/2)/n  Formula (3).

By substituting the above Formula (1) into the above Formula (3), thefollowing Formula (4) can be obtained:tan(θ₃/2)=(m/n)·tan(θ₁/2)  Formula (4)

By substituting the above Formula (2) into the above Formula (4), thefollowing Formula (5) can be obtained:tan(θ₃/2)=sin(θ₂)·tan(θ₁/2)  Formula (5)

By modifying the above Formula (5), the following Formula (6) can beobtained:θ₃=2·tan⁻¹(sin(θ₂)·tan(θ₁/2))  Formula (6)

(Concrete Example of Slitting Blade)

As a slitting blade 72, an industrial precision knife “FBC4019G”manufactured by Kyocera Corporation, for example, can be used. Thespecifications of FBC4019G are as follows:

-   -   Material: FW25 (material constituted by an assembly of fine        particles)    -   Vickers hardness [Kg/mm^(2]:) 1700    -   Transverse intensity [MPa]: 3900    -   Fracture toughness [MPa·m^(1/2)]: 10.3    -   Linear expansion coefficient [1/° C.(×10⁻⁶)]: 5.5    -   Particle size [μm] of particles constituting blade edge E: 0.6    -   Length of blade edge E [mm]: 40    -   Width [mm]: 19    -   Thickness [mm]: 0.25    -   Cross-sectional angle θ₁ [°] of blade edge E: 25

<<Effect of Embodiment 1>>

The tangent-plane blade edge angle θ₃ is an angle at which a slittingblade 72 cuts in an original sheet S when slitting the original sheet S.Therefore, the tangent-plane blade edge angle θ₃ largely affects qualityof a slit separator. Then, in a case where the tangent-plane blade edgeangle θ₃ falls within the above-described range α, it is possible toobtain a good-quality slit separator.

The present invention also encompasses a slitting apparatus 6 (see (a)of FIG. 4) that includes cutting devices 7 (see (a) and (b) of FIG. 5)each including a slitting blade. A slitting blade 72 fixed by a holder71 is encompassed in the present invention as the tangent-plane bladeedge angle θ₃ is encompassed in the above-described range α.

(Equivalent Conditions Producing Same Effect)

The cross-sectional angle θ₁ and the mounting angle θ₂ only need to bein a range of values derived from a relationship represented by theabove Formula (5) while the tangent-plane blade edge angle θ₃ fallswithin the range α. In such a case also, it is possible to obtain agood-quality slit separator.

(Effect Obtained by Shape of Slitting Blade)

As has been described, the shape of each of the slitting blades 72 isplane-symmetrical with respect to the plane a which is perpendicular tothe original sheet S and to the A-A cross section (see (a) and (b) ofFIG. 7). That is, the cross-sectional shape of each of the slittingblades 72 is plane-symmetrical with respect to a plane, the plane being(i) perpendicular to a plane including the original sheet S (plane onwhich the blade edge E is in contact with the original sheet S) and (ii)parallel to the direction D which is a conveyance direction in which theoriginal sheet S is conveyed. This makes it possible to obtain slitseparators having respective end surfaces which have uniform shapes.

(Slit separator production method, separator roll production method, anduse as slitting apparatus)

The present invention also encompasses a slit separator productionmethod including each step involved in the above-described separatorslitting method.

The present invention also encompasses a separator roll productionmethod including each step involved in the above-described separatorslitting method.

The present invention also encompasses the slitting apparatus 6(separator slitting apparatus) which realizes the above-describedseparator slitting method.

(Appearance of Fuzziness)

FIG. 15 is a set of views for describing how fuzziness occurs on theseparator 12 and the separator roll 10. (a) of FIG. 15 is a front viewof the separator roll 10. (b) of FIG. 15 is a side view of the separatorroll 10. (c) of FIG. 15 is an enlarged view of an area G shown in (a) ofFIG. 15. In the following description, a separator 12 is a slitseparator.

As illustrated in (a) and (b) of FIG. 15, the separator roll 10 includesa core 8 having an outer circumferential surface 81 a on which theseparator 12 is wound. The core 8 includes an outer cylinder part 81, aninner cylinder part 82, and ribs 83. The core 8 is identical in functionto the above-described cores u and l.

The above-described “fuzz” occurs on side parts, which are slit parts,of the separator 12. As illustrated in (c) of FIG. 15, in a case wherethe separator 12 is wounded on the core 8, fuzzes 12 a appear on an endsurface of the side parts of the separator roll 10.

(Advantages of Small Amount of Fuzziness)

If the fuzzes 12 a are scattered when, for example, the separator 12 iswound off from the separator roll 10, then there is a risk of adverselyaffecting a battery to be produced by use of the separator 12. Inaddition, appearances of the separator roll 10 and of the separator 12are impaired as illustrated in (c) of FIG. 15. The separator 12 is alsolinearly slit in an MD direction. In this case, there is a risk thattears occur from the fuzzes 12 a when tensile force is applied to theseparator 12. Furthermore, in a case where the fuzzes 12 a are mixed induring battery production, separators 12 overlap each other at partswhere the fuzzes 12 a are mixed in, and therefore the parts end uphaving higher resistance than do other parts therearound. This causeslocal variations in electric current density. Therefore, the fuzzes 12 amay cause (i) cathode degradation of a battery and (ii) generation ofdendrite. With the configuration of Embodiment 1, it is possible tosuppress the occurrence of such fuzzes 12 a.

[Embodiment 2]

The following discusses Embodiment 2 of the present invention withreference to FIGS. 10 to 13. Note that, for convenience, membersidentical in function to the members in the above-described embodimentare given the same reference signs, and their descriptions will beomitted (the same is true of the subsequent embodiments).

<<Other Separator Slitting Methods and their Effects>>

(Circular Slitting Blade)

FIG. 10 is a front view illustrating a configuration of a slitting blade72 a for use in a separator slitting method in accordance withEmbodiment 2.

As illustrated in FIG. 10, the slitting blade 72 a includes a blade edgeEa which, is a circular blade having a shape of a circular are(arc-shaped). A radius r is a radius of the circular arc. A length 1 is(i) a length of a part of the slitting blade 72 a, which part falls on aplane including the original sheet S and (ii) a length measured in adirection D. In this case, an entry angle θ_(2a), which is an anglebetween (i) a circular-arc-shaped tangent (tangent plane) at a point efrom which the slitting blade 72 a slits the original sheet S and (ii)the original sheet S, can be represented by the following Formula (7):cos(90°−θ_(2a))=(1/2)/r  Formula (7)

The above Formula (7) can be modified into the following Formula (8):90°−θ_(2a)=cos⁻¹((1/2)/r)  Formula (8)

The above Formula (8) can be modified into the following Formula (9):θ_(2a)=90°−cos⁻¹((1/2)/r)  Formula (9)

(Equivalent Conditions Producing Identical Effect as that of FlatSlitting Blade)

The fact that the entry angle θ_(2a) is formed between the blade edge Eaof the slitting blade 72 a and the original sheet S is equivalent to thefact that the mounting angle θ₂ is formed between the blade edge E ofthe above-described slitting blade 72 and the original sheet S. In thiscase, the A-A cross section shown in FIG. 10 corresponds to the A-Across section shown in (a) and (b) of FIG. 7. The B-B cross sectionshown in FIG. 10 corresponds to the B-B cross section shown in (a) and(b) of FIG. 8.

(Slitting by Use of Single-Beveled Slitting Blade)

FIG. 11 is a set of cross-sectional views illustrating a configurationof a slitting blade 72 b which is different from the slitting bladeillustrated in FIG. 10. (a) of FIG. 11 is a cross-sectional viewcorresponding to (b) of FIG. 7. (b) of FIG. 11 is a cross-sectional viewcorresponding to (d) of FIG. 9.

As illustrated in (a) of FIG. 11, the slitting blade 72 b is asingle-beveled blade. A cross section of the slitting blade 72 b matchesthe shape of a right half of the cross section of the slitting blades 72illustrated in (a) of FIG. 7. Note, however, that the cross section ofthe slitting blade 72 b is not limited to such a shape, but can be ashape with right and left sides reversed.

Note that a cross-sectional angle θ_(1a) of a blade edge E of theslitting blade 72 b is a half of the cross-sectional angle θ₁ of theslitting blades 72.θ_(1a)=θ₁/2  Formula (10)

In addition, as illustrated in (b) of FIG. 11, a tangent-plane bladeedge angle θ_(3a) of the slitting blade 72 b is half of thetangent-plane blade edge angle θ₃ of the slitting blades 72.θ_(3a)=θ₃/2  Formula (11)

By substituting the above Formulas (10) and (11) into the above Formula(6), the following Formula (12) can be obtained:θ_(3a)=tan⁻¹(sin(θ₂)·tan(θ_(1a)))  Formula (12)

By use of the above Formula (12), the tangent-plane blade edge angleθ_(3a) of the slitting blade 72 b, which is a single-beveled blade, canalso be calculated as is the case of the slitting blades 72 which is adouble-beveled blade.

(Slitting on Roller)

FIG. 12 is a front view illustrating a separator slitting method whichis different from the separator slitting method in which the slittingblade 72 a illustrated in FIG. 10 is used.

As illustrated in FIG. 12, an original sheet S is conveyed on a roller66 (conveying section). The roller 66 is provided with grooves in eachof which part of a blade edge E of a corresponding slitting blade 72 canbe inserted. A blade depth z is a depth of the part of the blade edge E,which part is inserted in the roller 66. A tangent plane p is a tangentplane on which a slitting position of the slitting blade 72 is incontact with the original sheet S.

In this case, an entry angle θ_(2b) formed between the slitting blade 72and the original sheet S being conveyed by the roller 66 can becalculated by use of the following Formula (13):θ_(2b)=cos⁻¹((r−z)  Formula (13)r: radius of roller 66

By using this angle θ in a manner similar to how the mounting angle θ₂is used, the tangent-plane blade edge angle θ₃ can be calculatedaccording to the above Formula (6).

Alternatively, the above-described slitting blade 72 b can be usedinstead of the slitting blade 72. In such a case also, by using theentry angle in a manner similar to how the mounting angle θ_(2b) isused, the tangent-plane blade edge angle θ_(3a) can be calculatedaccording to the above Formula (12).

It is thus possible to calculate a tangent-plane blade edge angle evenin a case of slitting an original sheet S on a roller.

(Slitting by Use of a Pair of Slitting Blades)

FIG. 13 is a front view illustrating another separator slitting methodwhich is different from the separator slitting method in which theslitting blade 72 a illustrated in FIG. 10 is used.

As illustrated in FIG. 13, each of pairs of slitting blades 72 c and 72d slits an original sheet S. The slitting blade 72 c and the slittingblade 72 d can be different from each other in size.

As each of slitting blades 72 c, an industrial precision knife“GUBD-09807T45DC15 (cross-sectional angle θ_(1a) of blade edge; 45°)”manufactured by Kyocera Corporation, for example, can be used. As eachof slitting blades 72 d, an industrial precision knife “GDBD-08005T”manufactured by Kyocera Corporation, for example, can be used.

FIG. 14 is a set of cross-sectional views illustrating a configuration,when viewed from a side, of the slitting blades 72 d which are lowerblades of the pairs of slitting blades 72 c and 72 d for use in theseparator slitting method illustrated in FIG. 13. (a) of FIG. 14 is aview illustrating an overall configuration. (b) of FIG. 14 is a viewenlarging an area C shown in (a) of FIG. 14.

As illustrated in (a) and (b) of FIG. 14, the slitting blades 72 d areincorporated in the roller 66. An outer diameter of each of the slittingblades 72 d is identical to that of the roller 66. Therefore, theoriginal sheet S is conveyed along outer circumferences 72 da of theslitting blades 72 d which rotate in coordination with the roller 66.

The slitting blades 72 d are each provided with a groove part 72 db. Theslitting blades 72 c, which are upper blades of the pairs of slittingblades 72 c and 72 d, are each a single-beveled blade. A blade edge Ecof each of the slitting blades 72 c is in contact with a correspondingone of side parts 72 dc, each of which is part of a side surface of agroove part 72 db of a slitting blade 72 d.

Note that, according to the law of cosines, the following Formulas (14)to (16), which concern a triangle having points Oc, Od and s shown inFIG. 13, can be worked out. Note an auxiliary line q is (i) an auxiliaryline for angle calculation and (ii) a straight line that passes twopoints at which the blade edge Ee of the slitting blade 72 c and theouter circumference 72 da of the slitting blade 72 d intersect.rc ² +OcOd ²−2·rc·OcOd·cos(θ_(2ce))=rd ²  Formula (14)rd ² +OcOd ²−2·rd·OcOd·cos(θ_(2cd))=rc ²  Formula (15)OcOd=rc+rd−n  Formula (16)rc: Radius of slitting blade 72 crd: Radius of slitting blade 72 dOcOd: Length between (i) the point Oc which is a center around which theslitting blade 72 c rotates and (ii) the point Od which is a centeraround which the slitting blade 72 d rotatesθ_(2cc): One entry angle between the auxiliary line q and the blade edgeEc of the slitting blade 72 cθ_(2cd): The other entry angle between the auxiliary line q and theouter circumference 72 da of the slitting blade 72 dz: Depth by which the slitting blade 72 c and the slitting blade 72 dare in contact with each other

By modifying the above Formulas (14) to (15), the following Formulas(17) to (18) can be obtained:θ_(2cc)=cos⁻¹((rc ² +OcOd ² −rd ²)/(2·rc·OcOd))  Formula (17)θ_(2cd)=cos⁻¹((rd ² +OcOd ² −rc ²)/(2·rc·OcOd))  Formula (18)

By using an entry angle “θ_(2cc)+θ_(2cd)”, which is a sum of said oneand the other entry angles θ_(2cc)·θ_(2cd), in a manner similar to howthe mounting angle θ₂ is used, it is possible to calculate thetangent-plane blade edge angle θ_(3a) according to the above Formula(12).

It is thus possible to calculate a tangent-plane blade edge angle evenin a case of slitting an original sheet S by use of pairs of slittingblades.

[Embodiment 3]

The following describes Embodiment 3 of the present invention.

<<Verification of Separator Slitting Method>>

In the following description, a type of separator to be slit, a type ofslitting blade (flat blade, circular blade), a cross-sectional shape(double-beveled blade, single-beveled blade) of a slitting blade, across-sectional angle θ₁ of a blade edge of a slitting blade, and amounting angle θ₂ of the slitting blade are variously changed so as tospecifically verify that quality of a slit separator depends on atangent-plane blade edge angle θ₃.

(Conditions in Which to Produce Slitting Film)

<Production of Polyolefin Porous Film>

In this verification, two types of separators are used. These separatorsare identical to the above-described “heat resistant separator”.Conditions, in which to produce a porous film constituting each of theheat resistant separators, are as follows.

70% by weight of a high molecular weight polyethylene powder (GUR4032(manufactured by Ticona Corporation)) and 30% by weight of polyethylenewax (FNP-0115 (manufactured by Nippon Seiro Co., Ltd.)) having aweight-average molecular weight of 1000 were prepared. Then, to a totalof 100 parts by weight of the high molecular weight polyethylene and thepolyethylene wax thus prepared, 0.4 part by weight of antioxidant(Irg1010 (manufactured by Ciba Specialty Chemicals Corporation)), 0.1part by weight of (P168 (manufactured by Ciba Specialty ChemicalsCorporation)), and 1.3 parts by weight of sodium stearate were added.Then, to 100% by volume of a resultant mixture, 38% by volume of calciumcarbonate (manufactured by Maruo Calcium Co., Ltd.) having an averagepar tide size of 0.1 μm was added. A resultant powder, while being apowder, was mixed with the use of a Henschel mixer. Then, the resultantpowder was melted and kneaded with the use of a biaxial kneader, so thata polyolefin resin composition was obtained. The polyolefin resincomposition was rolled with the use of a parr of rolls each having asurface temperature of 150° C., so that a sheet was produced. The sheetwas immersed in a hydrochloric acid aqueous solution (4 mol/L ofhydrochloric acid, 0.5% by weight of nonionic surfactant), so thatcalcium carbonate was removed. Then, a resultant sheet was stretched bya given multiplying factor at 105° C., so that a polyolefin porous filmhaving a thickness of 13.5 μm was obtained.

<Synthesis of Para-Aramid>

Conditions, in which to produce para-aramid for obtaining a heatresistant layer constituting each of the heat resistant separators, areas follows.

Para-aramid (poly (paraphenylene terephthalamide)) was produced with theuse of a 3-liter separable flask equipped with a stirring blade, athermometer, a nitrogen incurrent canal, and a powder addition port. Inthe flask in a sufficiently dry state, 2200 g of N-methyl-2-pyrrolidone(NMP) was introduced, and then 151.07 g of calcium chloride powder,which had been dried in vacuum at 200° C. for 2 hours, was added. Atemperature of the flask was then increased to 100° C., so that calciumchloride was completely dissolved in the NMP. A temperature of aresultant calcium, chloride solution was returned to room temperature,and then 68.23 g of paraphenylene diamine was added to and completelydissolved in the solution. 124.97 g of terephthalic acid dichloride wasdivided into 10 parts, which were then added at approximately 5-minuteintervals to the solution while the solution was maintained at 20° C.±2°C. The solution was matured while being stirred and maintained at 20°C.±2° C. for 1 hour, so that a para-aramid solution having a para-aramidconcentration of 6% by weight.

<Production of Heat Resistant Layer-Forming Slurry A>

Conditions, in which, to produce a heat resistant layer-forming slurry Afor obtaining the heat resistant layer, are as follows.

To 100 g of the para-aramid solution thus obtained, 243 g of NMP wasadded, and then a resultant solution was stirred for 60 minutes, so thata para-aramid solution having a para-aramid concentration of 1.75% byweight was obtained. Meanwhile, 6 g of alumina powder (Alumina C(manufactured by Nippon Aerosil Co., Ltd.), absolute specific gravity:3.2 g/cm³) and 6 g of alumina powder (Advanced Alumina AA-03(manufactured by Sumitomo Chemical Co., Ltd.), absolute specificgravity: 4.0 g/cm³) were mixed, so that 12 g of an alumina powdermixture was obtained. Then, 12 g of the alumina powder mixture was mixedwith the para-aramid solution having a para-aramid concentration of1.75% by weight, and then a mixture was stirred for 240 minutes, so thatan alumina powder-containing para-aramid solution was obtained. Then,the alumina powder-containing para-aramid solution was filtered with theuse of a 1000-mesh metal net. Then, to a resultant filtrate, 0.73 g ofcalcium oxide was added. Then, a resultant mixture was stirred for 240minutes for neutralization, and was then defoamed under reducedpressure, so that the heat resistant layer-forming slurry A wasobtained.

<Production of Laminated Porous Film A>

Conditions, in which to produce one of the above-described two types ofseparators, are as follows.

A roll (width: 300 mm, length: 300 m) of the polyolefin porous film wasattached to a wind-off machine. While the polyolefin porous film wasbeing pulled, the heat resistant layer-forming slurry A was applied toone surface of the polyolefin porous film, so that a laminated porousfilm A was continuously obtained.

To be specific, NMP was applied to a lower surface of the polyolefinporous film with the use of a micro-gravure coaler, and the heatresistant layer-forming slurry A was applied, in a prescribed thickness,to an upper surface of the polyolefin porous film with the use of a barcoater. Next, the film after being thus coated was allowed to passthrough the inside of a constant temperature/humidity chamber(temperature: 50° C., relative humidity: 70%), so that para-aramid wasprecipitated from the coated film. Then, the film was allowed to passthrough a water washing device (device having such a structure that aguide roll is set in a chamber (i) into which ion exchange water isinjected at an injection rate of 10 liters/minute and (ii) from whichthe ion exchange water filling the inside of the chamber is dischargedat a rate identical to the injection rate), so that NMP and calciumchloride were removed from the film.

Then, while hot air is blowing at the washed film with the use of adryer, the film was allowed to pass through a heat roll, so thatmoisture content was dried and removed. This caused a laminated porousfilm A, which had a thickness of 17.0 μm and was constituted bylaminating a heat resistant layer on one surface of the polyolefinporous film, was obtained.

A plate knife (manufactured by Kyocera Corporation, FBC4019G, blade edgecross-sectional angle: 25°) was attached to a slitting apparatus(manufactured by Hagihara Industries Inc., model: HDF-105S-1000). Then,in accordance with the conditions shown in Table 1, the laminated porousfilm A was slit while being moved along a roll having a diameter of 80mm.

<Production of Heat Resistant Layer-Forming Slurry B>

Conditions, in which to produce a heat resistant layer-forming slurry Bfor obtaining a heat resistant layer to be provided on the other one ofthe above-described two types of separators, are as follows.

To a medium in which a weight ratio between pure water and isopropylalcohol was 90:10, carhoxymethyl cellulose (CMC) (1110 (Manufactured byDaicel FineChem Ltd.), absolute specific gravity: 1.6 g/cm³) and aluminapowder (AKP3000 (manufactured by Sumitomo Chemical Co., Ltd.), absolutespecific gravity: 4.0 g/cm³) were added and mixed at a weight ratio of3:100 so that a solid content concentration was 28% by weight. Then, aresultant mixture was dispersed under high pressure, so that theresistant layer-forming slurry B was obtained.

<Production of Laminated Porous Film B>

Conditions, in which to produce the other separator, are as follows.

To a non-coated surface of the laminated porous film A, the heatresistant layer-forming slurry B was applied, so that a laminated porousfilm B was continuously obtained.

To be specific, the non-coated surface of the laminated porous film Awas subjected to a corona treatment. Then, the heat resistantlayer-forming slurry B was applied, with the use of a gravure coatingmachine, to the surface which was thus subjected to the coronatreatment, and then the surface was dried. This caused a laminatedporous film B, which had a thickness of 25.5 μm and was constituted bylaminating an aramid heat resistant layer on one surface of thepolyolefin porous film and by laminating a heat resistant layer(constituted by an alumina powder) on the other surface of thepolyolefin porous film, was obtained.

(Slitting Conditions)

TABLE 1 Tangent- plane Cross- blade Blade sectional Mounting edge Filmdepth z angle θ1 angle θ2 angle θ3 Fuzziness type (mm) (°) (°) (°)amount Ex. 1 A 1.0 25 12.8 5.6 Grade A Ex. 2 B 0.5 45 12.2 11.9 Grade AEx. 3 B 1.0 45 17.3 16.5 Grade A Ex. 4 A 0.5 60 12.2 20.1 Grade A Ex. 5B 2.0 45 24.5 22.5 Grade B Ex. 6 A 1.0 60 17.3 27.2 Grade B C.E. 1 A 0.225 5.7 2.5 Grade C C.E. 2 A 2.0 60 24.5 35.7 Grade C <Abbreviations>Ex.: Example C.E.: Comparative Example

Table 1 shows the verification results indicating that quality of a slitseparator (laminated porous film A or B after being slit) depends on atangent-plane blade edge angle Θ₃.

As shown in Table 1, the verification was performed by use of eightexamples (Examples 1 through 6, Comparative Examples 1 and 2). In regardto “Example 1” on the first row of Table 1, numerical values provided incolumns to the right of the leftmost column indicate numerical valuesobtained in Example 1. The same principle also applies to the otherexamples.

“Film type” indicates whether a slit separator is the above-describedlaminated porous film A or B.

“Blade depth z”, “Cross-sectional angle θ₁”, “Mounting angle θ₂”, and“Tangent-plane blade edge angle θ₃” are as described in the aboveembodiments.

“Fuzziness amount” indicates an amount of fuzziness that occurred atslit parts of a slit separator. “Grade A” indicates that the -quality ofa slit separator is excellent (there is no visible fuzziness). “Grade B”indicates that there is a small amount of fuzziness on a slit separator.“Grade C” indicates that there is a large amount of fuzziness on a slitseparator (there are more than one occurrences of visible fuzziness).

<Example 1 and Comparative Example 1>

These are examples in each of which (i) a plate knife (manufactured byKyocera Corporation, FBC4019G, blade edge cross-sectional angle: 25°)was attached to a slitting apparatus (manufactured by HagiharaIndustries Inc., model: HDF-105S-1000) and then (ii) in accordance withthe conditions shown in Table 1, the laminated porous film A was slitwhile being moved along a roll having a diameter of 80 mm.

<Examples 2, 3 and 5>

These are examples in each of which (i) gable blades (manufactured byKyocera Corporation, upper blade: GUBD-09807T45DC15 (blade edgecross-sectional angle: 45°) and a lower blade: GDBD-08005T) wereattached to a slitting apparatus (manufactured by Hagihara IndustriesInc., model: HDF-924-1900) and then (ii) in accordance with theconditions shown in Table 1, the laminated porous film B was slit whilebeing moved along the lower blade.

<Examples 4 and 6 and Comparative Example 2>

These are examples in each of which (i) gable blades (manufactured byKyocera Corporation, upper blade: GUBD-09807T60DC15 (blade edgecross-sectional angle: 60°), lower blade: GDBD-08005T) were attached toa slitting apparatus (manufactured by Hagihara Industries Inc., model:HDP-924-1900) and then (ii) in accordance with the conditions shown inTable 1, the laminated porous film A was slit while being moved alongthe lower blade.

(Other Slitting Conditions)

Note that an upper blade of gable blades is a single-beveled blade.Therefore, in Examples 2 to 6 and Comparative Example 2 in each of whichsuch gable blades are used, the tangent-plane blade edge angle θ₃ isθ_(3a) which is a value obtained by substituting the cross-sectionalangle θ₁ into θ_(1a) of the above Formula (12).

Note also that a conveyance speed of a separator at a part at which theseparator is slit is not less than 50 m/min and not more than 100 m/min.Note also that a take-up tensile force of the separator is not less than30 N/m and not more than 90 N/m.

<<Verification Results of Separator Slitting Method>>

The tangent-plane blade edge angle θ₃ is preferably not less than 3° andnot more than 35°, more preferably not less than 3° and not more than21°, and even more preferably not less than 5° and not more than 21°.

Specifically, the fuzziness amounts in Examples 1through 6 are each atthe grade A or B. Meanwhile, the fuzziness amounts in ComparativeExamples 1 and 2 are each at the grade C. This means that in a casewhere the tangent-plane blade edge angle θ₃ is in a range of not lessthan 3° to not more than 35°, it is possible to obtain a good-qualityslit separator having a small amount of fuzziness at a slit part thereof

In particular, the fuzziness amounts in Examples 1 to 4 are each at thegrade A. This means that in a case where the tangent-plane blade edgeangle θ₃ is in a range of not less than 5° to not more than 21°, it ispossible to obtain a good-quality slit separator having a smaller amountof fuzziness at a slit part thereof.

The quality of a slit separator thus depends on a tangent-plane bladeedge angle θ₃. In other words, it can be said that as long as thetangent-plane blade edge angle θ₃ remains at the identical value, it ispossible to obtain a slit separator of the identical quality even if anyof the following changes: a type of a separator to be slit; a type of aslitting blade (flat blade, circular blade); a cross-sectional shape(double-beveled blade, single-beveled blade) of a slitting blade, across-sectional angle θ₁ of a blade edge of the slitting blade; and amounting angle θ₂ of the slitting blade.

[Embodiment 4]

The following description will discuss Embodiment 4 of the presentinvention.

<<Configurations for Maintaining Consistent Tangent-Plane Blade EdgeAngles Among a Plurality of Slitting Blades>>

FIG. 16 is a set of schematic views each illustrating a configurationfor maintaining consistent tangent-plane blade edge angles θ₃ among aplurality of slitting blades in accordance with Embodiment 4. (a) to (e)of FIG. 16 each illustrate a configuration in which circular slittingblades 72 c are used. (f) and (g) of FIG. 16 each illustrate aconfiguration in which flat slitting blades 72 are used.

As illustrated in (a) of FIG. 16, in a case of circular slitting blades72 c, it is possible to maintain consistent tangent-plane blade edgeangles θ₃ among the circular slitting blades 72 c by attaching, to asingle axis 73, a plurality of slitting blades 72 c.

Note that as slitting continues, slitting blades 72 c are eachincreasingly abraded. In addition, a defect M such as chipping occurs toa slitting blade (s) 72 c in some cases. As illustrated in (b) of FIG.16, if only a slitting blade 72 c suffering a defect is replaced withanother one, then there is an imbalance in size between (i) a slittingblade 72A which is said another one and (ii) the other slitting blades72 c which have been abraded due to slitting. In this case, there isalso an imbalance in tangent-plane blade edge angle θ₃ between theslitting blade 72A and the slitting blades 72 c. Furthermore, asillustrated in (c) of FIG. 16, even in a case where a slitting blade 72c suffering the defect is ground so as to be restored, there is animbalance in tangent-plane blade edge angle θ₃ between (i) a slittingblade 72B which is the ground slitting blade 72 c and (ii) the otherslitting blades 72 c which have not been ground.

As illustrated in (d) of FIG. 16, an original sheet S, which is conveyedin a direction D and which has a prescribed width, is slit by slittingblades 72 c, the number of which slitting blades 72 c corresponds to theprescribed width. As illustrated in (e) of FIG. 16, of all slittingblades 72 c, only slitting blades 72C whose blades touch the originalsheet S become abraded due to the slitting. Therefore, the number ofslitting blades 72 c is preferably an appropriate number whichcorresponds to the width of the original sheet S to be slit, so that theslitting blades 72 c are consistent with each other in terms of (i) theextent of abrasion and (ii) the frequency of defect occurrences. Inaddition, slitting blades 72 c for slitting an original sheet S arepreferably replaced all at once.

As illustrated in (f) of FIG. 16, even in a ease of flat slitting blades72, it is also possible to maintain consisterit tangent-plane blade edgeangles θ₃ among the flat slitting blades 72 by attaching a plurality ofslitting blades 72 to a single axis 73 and (ii) moving the plurality ofslitting blades 72 all at once. As illustrated in (g) of FIG. 16,slitting blades 72 are attached to a rotation axis 73 a preferably by ascrew or the like so that the slitting blades 72 are rotatable. In sodoing, it is more preferable to provide a stopper 73 b so as to specifya rotation range of the slitting blades 72 so that the slitting blades72 each do not rotate up to, for example, a position indicated bytwo-dot chain lines.

(Change in Tangent-Plane Blade Edge Angle)

FIG. 17 is a schematic view describing a configuration for makingtangent-plane blade edge angles θ₃ of slitting blades substantiallyidentical with each other. (a) of FIG. 17 illustrates an example inwhich a position and/or angle of the slitting blade 72 which is a flatblade is changed. (b) of FIG. 17 illustrates an example in which thetangent-plane blade edge angle θ₃ of the slitting blade 72 is changed.(c) of FIG. 17 illustrates a method for producing a slit separator byslitting the original sheet S in such a manner as to make thetangent-plane blade edge angles θ₃ of a plurality of various slittingblades substantially identical with each other, and (d) of FIG. 17illustrates a method for producing a slit separator by further slittinganother original sheet S.

As illustrated by two-dot chain lines in (a) of FIG. 17, when theposition and/or angle of the slitting blade 72 is changed, the mountingangle θ₂ is also changed. Consequently, as illustrated in (b) of FIG.17, the tangent-plane blade edge angle θ₃ of the slitting blade 72 getssmaller to be a tangent-plane blade edge angle θ_(3A) or gets larger tobe a tangent-plane blade edge angle θ_(3B).

In this case, by calculating the tangent-plane blade edge angle θ₃ bysubstituting the cross-sectional angle θ₁ of a blade edge E of theslitting blade 72 and the mounting angle θ₂ after the change into theFormula (6), it is possible to calculate the tangent-plane blade edgeangles θ_(3A) and θ_(3B).

Furthermore, as illustrated in (a) of FIG. 16, the cross-sectional angleθ₁ is changed due to abrasion of the slitting blade 72 and a defectfound in the slitting blade 72. As can be seen from the Formula (6),when the cross-sectional angle θ₁ is changed, the tangent-plane bladeedge angle θ₃ is changed even if the mounting angle θ₂ is not changed.

Respective tangent-plane blade edge angles of the slitting blade 72 awhich is a circular blade, the slitting blade 72 b which is asingle-beveled slitting blade, and the pair of slitting blades 72 c and72 d are changed similarly with the tangent-plane blade edge angle θ₃ ofthe slitting blade 72. Various types of the slitting blades above willbe hereinafter referred to merely as “slitting blade”.

(Method for Producing Slit Separator Whose Change in Tangent-Plane BladeEdge Angle is Prevented)

As illustrated in (c) of FIG. 17, the method for producing a slitseparator in accordance with Embodiment 4 includes the step S101 (firstconveying step) of conveying the original sheet S and the step S102 a(first slitting step) of slitting the original sheet S with use of aplurality of slitting blades.

In this configuration, in the step S102 a, the tangent-plane blade edgeangles θ₃ of a plurality of slitting blades are within the range of theangle θ_(c)±Δ.

The plurality of slitting blades indicate, for example, a plurality ofslitting blades 72 illustrated in (b) of FIG. 6 or (f) of FIG. 16 or aplurality of slitting blades 72 c illustrated in (a) of FIG. 16.

The angle θ_(c) is a target value of the tangent-plane blade edge anglesθ₃ of the plurality of slitting blades as above, and is within, forexample, the above range α.

Δ is a positive number and is a value indicating a range within whichthe tangent-plane blade edge angle θ₃ is changed from the angle θ_(c).In a case where Δ is so small that the angle (θ_(c)−Δ) and the angle(θ_(c)+Δ) are each within a predetermined range (e.g. the aforementionedrange α), tangent plane blade edge angles θ₃ of a plurality of slittingblades can be treated as being a substantially identical angle θ_(c).

In the step S102 a, tangent-plane blade edge angles θ₃ of a plurality ofslitting blades may be within a range of not less than the angle(θ_(c)−Δ_(A)) and not more than the angle (θ_(c)+Δ_(B)). In this case,Δ_(A) and Δ_(B) are 0 of a positive number and are different from eachother. In a case where Δ_(A) and Δ_(B) are so small that the angle(θ_(c)−Δ_(A)) and the angle (θ_(c)+Δ_(B)) are each within apredetermined range (e.g. aforementioned range α), tangent-plane bladeedge angles θ₃ of a plurality of slitting blades can be treated as beinga substantially identical angle θ_(c).

(Target Value and Variable Range of Tangent-Plane Blade Edge Angle)

As described above, tangent-plane blade edge angles θ₃ of a plurality ofslitting blades being substantially identical with each other is equalto presence of the angle θ_(c) and Δ which allow the angle (θ_(c)−Δ) andthe angle (θ_(c)+Δ) to be each within a predetermined range.

The predetermined range herein is such a range that when thetangent-plane blade edge angles θ₃ are within that range, a good-qualityslit separator having a small amount of fuzziness at a slit part thereofcan be obtained. For example, the range of not less than 11.9° and notmore than 20.1° which is a range of the tangent-plane blade edge angleθ₃ shown in Examples 2-4 of Table 1 can be considered as thepredetermined range.

For example, the angle θ_(c) is set to 16.0° which is an average of11.9° and 20.1°. Furthermore, Δ is set to 4.1° which is a differencebetween 20.1° and 16.0°. In this case, the angle (θ_(c)−Δ) is 11.9°. Theangle (θ_(c)+Δ) is 20.1°. Accordingly, the angle θ_(c) and Δ which allowthe angle (θ_(c)−Δ) and the angle (θ_(c)+Δ) to be each within apredetermined range are present.

(Step of Slitting Original Sheet with Use of a Plurality of SlittingBlades)

The step S102 a which is a step of slitting the original sheet S withuse of a plurality of slitting blades is specifically a step of slittingthe original sheet S by causing the plurality of slitting blades to cutinto the original sheet S such that the tangent-plane blade edge anglesθ₃ are substantially identical with each other.

In other words, the step S102 a is a step of slitting the original sheetS by causing a plurality of slitting blades to cut into the originalsheet S such that the tangent-plane blade edge angles θ₃ are each withina predetermined range.

The predetermined range may be such a range that, for example, when thetangent-plane blade edge angles θ₃ are within that range, a good-qualityslit separator having a small amount of fuzziness at a slit part thereofcan be obtained.

Causing a plurality of slitting blades to cut into the original sheet Ssuch that the tangent-plane blade edge angles θ₃ are each within apredetermined range indicates causing a plurality of slitting blades,each of which has a cross sectional angle θ₁ within a range that meetsthe relation of the aforementioned Formula (5) (e.g. not less than 45°and not more than 60°) and has a mounting angle θ₂ within a range thatmeets the relation of the Formula (5) (e.g. not less than 12.2° and notmore than 17.3°) to cut into the original sheet S, with thetangent-plane blade edge angles θ₃ each being within a predeterminedrange (e.g. not less than 11.9° and not more than 20.1°).

(Method for Producing Slit Separator, Which Maintains ConsistentAbrasion State of Slitting Blade)

As illustrated in (d) of FIG. 17, the method for producing a slitseparator in accordance with the present embodiment may further include:a step S101 a (second conveying step) which is a step of conveying aporous original sheet which is other than the original sheet S conveyedin the aforementioned step S101 and which has the same width as that ofthe original sheet S conveyed in the step S101; and a step of S102 b(second slitting step) which is a step of slitting the other originalsheet by causing a plurality of slitting blades to cut into the otheroriginal sheet.

In the step S102 a, as illustrated in (d) of FIG. 16, the original sheetS is slit with use of a part of the plurality of slitting blades.

In the step S102 b, the original sheet conveyed in the step S101 a isslit with use of slitting blades identical with those having slit theoriginal sheet S in the step S102 a. That is, in order that a pluralityof slitting blades have constant degree of abrasion or constantfrequency of defects, the number of slitting blades used is anappropriate number corresponding to the width of the original sheet S tobe slit in the step S102 a and the width of the other original sheet tobe slit in the step S102 b.

In this case, the tangent-plane blade edge angles θ₃ of the slittingblades used for slitting are each within a range of the angle θ_(c)±Δ.

<<Effects of the Present Embodiment>>

As illustrated in FIG. 16, by fixing slitting blades, it is possible toprevent positions and angles of slitting blades with respect to anoriginal sheet S from being accidentally changed during an operation ofa slitting apparatus 6 (see FIG. 4). This configuration is advantageousparticularly in a case where a separator original sheet including aninorganic filler(s) is to be slit, because slitting blades of such aseparator original sheet are quickly abraded.

In the method for producing a slit separator illustrated in (c) of FIG.17, in a case where the original sheet S which is porous is slit,fuzziness can easily occur at a slit part(s) because of porousness ofthe original sheet S.

In this case, the tangent-plane blade edge angles θ₃ affect fuzzinessthat occurs at the slit part of the slit separator. The fuzziness can beeffectively suppressed by causing the tangent-plane blade edge angles θ₃to be substantially identical with each other (θ_(c)−Δ≤θ₃≤θ_(c)+Δ).

With the method for producing a slit separator, it is possible toobtain, all at once, a plurality of good-quality slit separators with asmall amount of fuzziness at slit parts thereof.

The Δ is preferably not more than 5°, more preferably not more than 3°,and further more preferably not more than 1°.

In this case, since slit parts of the plurality of slit separators havesubstantially identical fuzziness, quality of the plurality of slitseparators is stable. As Δ is smaller, the slit parts of the pluralityof slit separators have further identical fuzziness, so that the qualityof the plurality of slit separators is more stable.

With the method for producing a slit separator as illustrated in (d) ofFIG. 17, it is possible to use the same slitting blades both for aplurality of slitting blades to slit the original sheet S in the stepS102 a and for a plurality of slitting blades to slit other originalsheet in the step S102 b. This allows the slitting blades to beconsistent with each other in terms of the extent of abrasion or thefrequency of defect occurrences.

As illustrated in (b) of FIG. 6, a slit separator s1 (slit film) isobtained by slitting an original sheet with use of adjacent two slittingblades out of a plurality of slitting blades. Consequently, it ispossible to obtain a better-quality slit separator with a small amountof fuzziness at a slit part thereof at both ends of the slit separators1 in a width direction.

SUMMARY

A method for producing a slit separator in accordance with Aspect 1 ofthe present invention includes: a conveying step of conveying a batteryseparator original sheet which is porous; and a first slitting step ofslitting the battery separator original sheet by causing a plurality ofslitting blades to cut into the battery separator original sheet suchthat a plurality of slitting blade edge angles in a tangent plane, onwhich a slitting position is in contact with the battery separatororiginal sheet, are substantially identical with each other.

In a case where a battery separator original sheet which is porous isslit, fuzziness can easily occur at a slit part(s) because of porousnessof the battery separator original sheet.

In this case, a slitting blade edge angle (hereinafter, referred to as“tangent-plane blade edge angle”) in a tangent plane, on which aslitting position is in contact with a battery separator original sheet,affects fuzziness that occurs at the slit part of the separator. Bycausing the tangent-plane edge angles to be substantially identical witheach other, it is possible to effectively prevent fuzziness.

With the method, it is possible to obtain, all at once, a plurality ofgood-quality slit separators with a small amount of fuzziness at a slitpart thereof.

It is preferable to arrange the method such that in the first slittingstep, a film obtained by slitting the battery separator original sheetis obtained by slitting with use of adjacent two slitting blades out ofthe plurality of slitting blades.

With the method, it is possible to obtain a better-quality slitseparator with a small amount of fuzziness at a slitting part, thereofat both ends of the slit, film in a width direction.

It is preferable to arrange the method such that the plurality ofslitting blades are attached to a single axis positioned fixedly withrespect to the battery separator original sheet.

With the method, the plurality of slitting blades are positioned fixedlywith respect to the battery separator original sheet via the singleaxis. Consequently, it is possible to surely cause the plurality ofslitting blades to cut into the battery separator original sheet suchthat tangent-plane blade edge angles of the plurality of slitting bladesare substantially identical with each other.

It is preferable to arrange the method such that at least one of theplurality of slitting blades is a flat blade and is rotatably attachedto the axis.

With the method, it is possible to cause the flat blade rotatablyattached to the axis to rotate and adjust the angle of the flat blade.This allows fine adjustment such that tangent-plane blade edge angles ofslitting blades are substantially identical with each other.

It is preferable to arrange the method such that a rotational angle ofsaid at least one slitting blade rotatably attached to the axis islimited by a stopper positioned fixedly with respect to the axis.

With the method, it is possible to stop the slitting blade rotatablyattached to the axis and limit the angle of the slitting blade. Thissurely allows adjustment such that tangent-plane blade edge angles ofthe slitting blades are substantially identical with each other.

It is preferable to arrange the method such that in the first slittingstep, two or more slitting blades being a part of the plurality ofslitting blades slit the battery separator original sheet, and themethod further comprises: a second conveying step of conveying otherbattery separator original sheet which is porous and has a same width asthat of the battery separator original sheet; and a second slitting stepof slitting the battery separator original sheet by causing said two ormore slitting blades to cut into the other battery separator originalsheet such that slitting blade edge angles of said two or more slittingblades in a tangent plane, on which a slitting position is in contactwith the other battery separator original sheet, are substantiallyidentical with each other.

With the method, it is possible to use the same slitting blades both fora plurality of slitting blades to slit the battery separator originalsheet in the first slitting step and for a plurality of slitting bladesto slit other battery separator original sheet in the second slittingstep. This allows the slitting blades to be consistent with each otherin terms of the extent of abrasion or the frequency of defectoccurrences.

It is preferable to arrange the method so as to further include the stepof replacing the plurality of slitting blades all at once.

With the method, ii is possible to replace, all at once, slitting bladeswhich are abraded to the same extent or to which defect is likely tooccur to the same extent.

The method may be arranged such that the battery separator originalsheet contains inorganic filler.

In a case where a battery separator original sheet containing inorganicfiller is slit, slitting blades are abraded with a faster pace. However,with the method, even in the case where such a battery separatororiginal sheet is slit, it is possible to obtain, all at once, aplurality of good-quality slit separators with a small amount offuzziness at slit parts thereof.

Furthermore, by fixing a slitting blade with use of the aforementionedstopper, it is possible to prevent erroneously change the position orangle of the slitting blade with respect to the battery separatororiginal sheet. This method is useful particularly in the case where thebattery separator original sheet containing inorganic filler is slitbecause in such a case a slitting blade is abraded with a faster pace.

It is preferable to arrange the method such that in the first slittingstep, the battery separator original sheet is slit by causing theplurality of slitting blades to cut into the battery separator originalsheet such that the plurality of slitting blade edge angles are eachwithin a predetermined range.

It is preferable to arrange the method such that in the first slittingstep, the battery separator original sheet is slit fay causing theplurality of slitting blades, each of which has a cross sectional angleθ₁ within a range that meets Formula (5) below and has a mounting angleθ₂ within a range that meets Formula (5) below, to cut into the batteryseparator original sheet, with the plurality of slitting blade edgeangles being θ₃ within a predetermined range.tan(θ₃/2)=sin(θ₂)·tan(σ₁/2)  Formula (5)

It is preferable to arrange the method such that the predetermined rangeof the plurality of slitting blade edge angles is a range that enablesthe method to produce a good-quality slit separator with a small amountof fuzziness at a slit part thereof.

A method for producing a separator roll in accordance with Aspect 2 ofthe present invention includes: each of the steps recited in theaforementioned method for producing a slit separator; and a winding stepof winding, around a core, a separator obtained by slitting the batteryseparator original sheet.

When a slit separator obtained by slitting a battery separator originalsheet is wound around a core, fuzz occurring on side parts of the slitseparator in a width direction appears on an end surface of the sideparts of a separator roll.

With the method, it is possible to obtain, all at once, a plurality ofgood-quality separator rolls with a small amount of fuzziness on an endsurface of the side parts of each of the separator rolls.

[Referential Example]

A method for producing a slit separator in accordance with ReferentialAspect 1 of the present invention includes: a conveying step ofconveying a battery separator original sheet which is porous; and aslitting step of slitting the battery separator original sheet bycausing a slitting blade to cut into the battery separator originalsheet such that a slitting blade edge angle in a tangent plane, on whicha slitting position is in contact with the battery separator originalsheet, is in a range of not less than 3° to not more than 35°.

The battery separator original sheet which is porous has a tendencythat, due to its porosity, a slit part thereof is likely to havefuzziness when the battery separator original sheet is slit.

The inventors found that (i) a slitting blade edge angle (hereinafter,referred to as “tangent-plane blade edge angle”) in a tangent plane, onwhich a slitting position is in contact with a battery separatororiginal sheet, affects fuzziness that occurs at the slit part of theseparator and (ii) the fuzziness can be effectively suppressed bycausing the tangent-plane blade edge angle to be in a range of not lessthan 3° to not more than 35°.

With the method, it is possible to obtain a good-quality slit separatorhaving a small amount of fuzziness at a slit part thereof.

The slit separator production method is preferably configured such thatthe slitting blade edge angle is not more than 28°.

With the method, it is possible to obtain a good-quality slit separatorhaving a smaller amount of fuzziness at a slit part thereof.

It is more preferable to arrange the method such that the slitting bladeedge angle is a range of not less than 5° to not more than 21°.

With the method, it is possible to obtain a superior-quality slitseparator having an even smaller amount of fuzziness at a slit partthereof.

The method may be arranged such that the battery separator originalsheet has, at the slitting position, a curved surface that is convexedtoward the slitting blade.

With the method, the tangent-plane blade edge angle is determined by alength at which the blade edge of the slitting blade is inserted intothe curved surface. This allows the tangent-plane blade edge angle to beeasily adjusted.

The method may be arranged such that a blade edge of the slitting bladeis arc-shaped.

With the method, the tangent-plane blade edge angle Is determined by alength at which the blade edge of the slitting blade is inserted intothe battery separator original sheet being conveyed. This allows thetangent-plane blade edge angle to be easily adjusted.

The method may be arranged such that a shape of the blade edge of theslitting blade is plane-symmetrical with respect to a plane, the planebeing (i) perpendicular to the tangent plane and (ii) parallel to adirection in which the battery separator original sheet is conveyed.

With the method, it is possible to obtain slit separators whoserespective end surfaces, at which the slit separators have been slit,are closer to being uniform.

A separator roll production method in accordance with Referential Aspect2 of the present invention includes: each of the steps recited in theslit separator production method; and a winding step of winding, arounda core, a separator which has been slit.

With the method, a separator roll, which is made up of a core and aseparator wound around the core, is obtained. In this case, a slit partof the separator corresponds to a surface of the roll, which surface islocated on a side-surface side of the core. By use of theabove-described slit separator production method, it is possible toobtain a good-quality slit separator having a small amount of fuzzinessat a slit part thereof. This makes it possible to obtain a good-qualityseparator roll having a surface on which there is a small amount offuzziness.

A separator slitting method in accordance with Referential Aspect 3 ofthe present invention includes: a conveying step of conveying a batteryseparator original sheet which is porous; and a slitting step ofslitting the battery separator original sheet by causing a slittingblade to cut into the battery separator original sheet such that aslitting blade edge angle in a tangent plane, on which a slittingposition is in contact with the battery separator original sheet, is ina range of not less than 3° to not more than 35°.

A separator slitting apparatus in accordance with Referential Aspect 4of the present invention includes: a conveying section for conveying abattery separator original sheet which is porous; and a slitting bladefor slitting the battery separator original sheet, a blade edge angle ina tangent plane, on which a slitting position of the slitting blade isin contact with the battery separator original sheet, being in a rangeof not less than 3° to not more than 35°.

[Additional Remarks]

The present invention is not limited to the embodiments, but can bealtered by a skilled person in the art within the scope of the claims.An embodiment derived from a proper combination of technical means eachdisclosed in a different embodiment is also encompassed in the technicalscope of the present invention.

Industrial Applicability

The present invention can be used for (i) a method for slitting a filmin any direction, (ii) a method for producing a film roll, and (iii) afilm slitting apparatus.

REFERENCE SIGNS LIST

1 Lithium-ion secondary battery

3 Lithium ion

4 Heat resistant layer

6 Slitting apparatus (separator slitting apparatus)

7 Cutting device

12 Separator

66 Roller (conveying section)

71 Holder

72,72 a through 72 d Slitting blade

E,Ea,Ec Blade edge

P Pore

S Original sheet (separator)

S101 Step of conveying separator original sheet, first conveying step

S101 a Step of conveying other separator original sheet, secondconveying step

S102 Step of slitting separator original sheet

S102 a Step of slitting separator original sheet, first slitting step

S102 b Step of slitting separator original sheet, second slitting step

T Cross section (tangent plane)

θ₁,θ_(1a),θ₄ Cross-sectional angle

θ₂ Mounting angle

θ_(2a),θ_(2b) Entry angle

θ_(2cc),θ_(2cd) One entry angle

θ₃,θ_(3a) Tangent-plane blade edge angle

The invention claimed is:
 1. A method for producing a slit separator,comprising: a first conveying step of conveying a battery separatororiginal sheet which is porous; and a first slitting step of slittingthe battery separator original sheet in a direction of conveyance of thebattery separator original sheet by causing a plurality of slittingblades to cut into the battery separator original sheet such that aplurality of tangent-plane blade edge angles are substantially identicalwith each other, each of the plurality of tangent-plane blade edgeangles being a cross-sectional angle of a corresponding one of theplurality of slitting blades, the corresponding one of the plurality ofslitting blades expanding from its edge as a tip so as to have thecross-sectional angle on a plane which includes the battery separatororiginal sheet with which the edge is in contact, each of the pluralityof tangent-plane blade edge angles being in a range of not less than 3°and not more than 35°.
 2. The method as set forth in claim 1, wherein inthe first slitting step, a film obtained by slitting the batteryseparator original sheet is obtained by slitting with use of adjacenttwo slitting blades out of the plurality of slitting blades.
 3. Themethod as set forth in claim 1, wherein the plurality of slitting bladesare attached to a single axis positioned fixedly with respect to thebattery separator original sheet.
 4. The method as set forth in claim 3,wherein at least one of the plurality of slitting blades is a flat bladeand is rotatably attached to the axis.
 5. The method as set forth inclaim 4, wherein a rotational angle of said at least one slitting bladerotatably attached to the axis is limited by a stopper positionedfixedly with respect to the axis.
 6. The method as set forth in claim 1,wherein in the first slitting step, two or more slitting blades being apart of the plurality of slitting blades slit the battery separatororiginal sheet, and the method further comprises: a second conveyingstep of conveying a further battery separator original sheet which isporous and has a same width as that of the battery separator originalsheet; and a second slitting step of slitting the battery separatororiginal sheet by causing said two or more slitting blades to cut intothe further battery separator original sheet such that tangent-planeblade edge angles of said two or more slitting blades in a tangent planeare substantially identical with each other, the tangent plane being aplane which includes the further battery separator original sheet. 7.The method as set forth in claim 6, further comprising the step ofreplacing the plurality of slitting blades all at once.
 8. The method asset forth in claim 1, wherein the battery separator original sheetcontains inorganic filler.
 9. The method as set forth in claim 1,wherein in the first slitting step, the battery separator original sheetis slit by causing the plurality of slitting blades, each of which has across sectional angle θ1 within a range that meets Formula (5) below andhas a mounting angle θ2 within a range that meets Formula (5) below, tocut into the battery separator original sheet, with the plurality oftangent-plane blade edge angles being θ3 within a predetermined rangetan(θ3/2)=sin(θ2)·tan(θ1/2)  Formula (5).
 10. The method as set forth inclaim 1, wherein the range of not less than 3° and not more than 35° ofeach of the plurality of tangent-plane blade edge angles is a range thatenables the method to produce a good-quality slit separator with a smallamount of fuzziness at a slit part thereof.
 11. A method for producing aseparator roll, comprising: each of the steps recited in the method asset forth in claim 1; and a winding step of winding, around a core, aseparator obtained by slitting the battery separator original sheet.